Hot Water Cylinders Part 2

Continuing on from our earlier article Hot Water Introduction, we briefly mentioned mains pressure hot water cylinders and low pressure hot water cylinders.

Lets take a closer look at low pressure electric hot water cylinders.

Low pressure hot water cylinders particularly those with open vents are still quite common in colder climates due to the fact that wetback heating options are often attached and these need to be vented to the open air.

In these setups the cold water is usually supplied in this manner (there are variations) – mains supply from the street to the house – high pressure cold water feed to a ceiling tank controlled by a ball cock. This ceiling tank can be either a copper or plastic tank usually about 135 litres in capacity.

From here the water is gravity fed to the low pressure hot water cylinder where it is heated as required. When hot water is drawn off or used, cold water gravity feeds back into the cylinder which pushes the hot water through the pipes using the gravity affect.

Water flow is dictated by the height of the ceiling tank (also called header tank) above the hot water outlet – we usually measure this from the highest outlet which is usually the shower head, so if the ceiling tank is 2 metres above the shower head outlet we have 2 metres of head or roughly 20kpa around 3 psi – which is pretty low. With this type of system, you need to make sure that you have the correct type of shower faucets and taps as using fixtures designed for high pressure will simply not work.

Maintenance
With this type of system there is relatively little maintenance as not a lot of valve ware is installed. The ceiling tank is required to be installed over a safe tray which drains to the exterior of your house, so in the event of a leak or ballcock malfunction and the tank overflows, the water is safely routed to the outside of your house, not through your ceiling. Check the following:

• Ceiling tank outlet shutoff – make sure this does in fact shutoff, should a leak occur in your hot water cylinder, you need to be able to shut of the water supply to your hot water cylinder.
• Ballcock – check to make sure that this is closing correctly, at the correct height inside the ceiling tank. If it doesn’t close off completely, simply replace the washer inside.Make sure the ball float is securely attached – the screw type balls can work themselves loose over a period of years.
• Look for leaks in and around the tank
• Check the ceiling tank overflow outside, make sure it is not blocked by a birds nest or other obstruction.
• Make the the lid on the ceiling tank is securely fastened – keep out dust and dirt
• Check for leaks around fittings on your hot water cylinder – these low pressure open vented hot water cylinders last for many many years – as there is no stress put on them by the use of pressure relief valves and the like

In the next part we will look at Low Pressure Valve Vented Hot Water Cylinders.